One type of a conventional phase adjusting system for a radio communication system such as a paging system comprises a plurality of transmitters each connected to a central station, and a plurality of receivers each connected for phase adjustment to the central station and positioned between corresponding two of the transmitters. The central station comprises a CPU for controlling the system, and a plurality of delay time setting circuits each provided on a line connected to a corresponding one of the transmitters. Among the transmitters, the sequential order of the phase adjustment is fixed beforehand, wherein a transmitter which plays a role for a standard in the phase adjustment is called "a reference", and a transmitter which is adjusted in phase is called "a target".
In operation, a transmitter which is No. 1 in the sequential order of the phase adjustment is regarded as the reference for the first phase adjustment, and a transmitter which is No. 2 therein is the target, so that signal is transmitted from the central station through the delay time setting circuit to the transmitter No. 2, then from the transmitter No. 2 to the corresponding receiver, and from the receiver back to the central station, and further signal is transmitted from the central station through the delay time setting circuit to the transmitter No. 1, then from the transmitter No. 1 to the corresponding receiver, and from the receiver back to the central station. In the central station, delay times are detected in the signals transmitted through the transmitters Nos. 1 and 2 for the reference and target. The difference of the delay times is calculated, so that a value corresponding to the difference is set in the delay time setting circuit for the target transmitter No. 2 to decrease the difference to a sufficient extent.
In the second phase adjustment, the transmitter No. 2 is for the reference, and a transmitter which is No. 3 in the sequential order is selected for the target, so that the same phase adjustment as in the first phase adjustment is performed between the transmitters Nos. 2 and 3. In this manner, all the transmitters are adjusted in phase.
In the above phase adjusting system, each of the transmitters comprises a memory for storing its own sequential order for the phase adjustment, so that one of the transmitters is turned on in accordance with the designation of the number in the sequential order from the central station, and turned off in accordance with the cease of the designation thereof. Therefore, the phase adjustment can be repeated sequentially only by designating the number in the sequential order.
In the conventional phase adjusting system, however, there is a disadvantage that it is difficult to change the sequential order of the phase adjustment because a content of the memory for each of the transmitters is inconvenient to be changed due to the fact that almost all of the transmitters are installed in stations having no staff for maintaining the stations. Even if the content of the memory is changed in the station by dispatching a staff thereto, a considerable time is consumed. During the time, therefore, the phase adjustment operation must be ceased, so that the change of delay times is not corrected.